The general description of the problem and objective is as follows. Large structures can be assembled from smaller discrete parts. This has several benefits including the mass production of parts, the assembly and disassembly of parts for repair or reconfiguration, and the automation of the assembly with robots. Robotic assembly is an existing technology which typically uses multi degree of freedom (DOF) robots for dexterity and complex maneuvering. One example is industrial robot arms used for car manufacturing. These robots require sophisticated control strategies, and they are typically fitted with varying end effectors for the tasks they perform (e.g., welding, tightening, painting). These robots can be mounted to linear gantries to increase the available build area for a given robot. However, this approach runs into issues for very large or complex structures.
This invention involves several key and unique problem characteristics. Discrete assembly of larger structures affords numerous opportunities to overcome the limitations of traditional robotic assembly approaches. The lattice structure in question is periodic and isotropic, so it provides a structured environment in which the robot operates. This can alleviate requirements for global positioning or vision systems, due to the fact that it only works within the 3D grid. In this sense, the structure is “digital”, in that it can be considered as a 1 or a 0—there is either structure or no structure.
There is prior art (i.e., prior techniques, methods, materials, and/or devices), but none that describe a Bipedal Isotropic Lattice Locomoting Explorer as described by the present invention. For example, there are relevant examples of robots that build lattice structures, robots that move in an inch work fashion, and robots that operate and manipulate discrete structures. Disadvantages or limitations of the prior art include: 1) Lattice building robots: the build volume of these gantry based robot platforms limits the scale of the object being built. Also reach is limited by the geometry of the robot arm or gantry system; 2) Inchworm robots: The main difference between the robot described by the present invention and existing bipedal inchworm robots is that it is a relative robot operating within a 3D isotropic lattice. This enables it to perform much more complex maneuvers while also enabling interaction and manipulation with the structure that other robots, attaching with means such as suction cups, would be unable to achieve; 3) Relative structure robots: these are not suitable for space applications due to the density of the structure.
Automated construction of large structures is desirable in numerous fields, such as infrastructure and aerospace [W. Whittaker, C. Urmson, P. Staritz, B. Kennedy, and R. O. Ambrose, “Robotics for assembly, inspection, and maintenance of space macrofacilities,” Am. Inst. Aeronaut. Astronaut., 2000]. The construction of large space structures has been a challenge due to the limitations of human-based extravehicular activity (EVA) and robot-based extravehicular robotics (EVR). Both approaches face problems regarding risk, throughput, and reliability [M. D. Rhodes, R. W. Will, and C. Quach, “Baseline Tests of an Autonomous Telerobotic System for Assembly of Space Truss Structures,” Langley, 1994] [M. Lake, W. Heard, J. Watson, and T. J. Collins, “Evaluation of Hardware and Procedures for Astronaut Assembly and Repair of Large Precision Reflectors,” Langley, 2000]. One approach is the autonomous robotic assembly of structures based on truss elements. This is an approach that has been proposed for decades [M. Mikulas and J. T. Dorsey, “An integrated in-space construction facility for the 21st century,” NASA Tech. Memo. 101515, 1988], [M. Mikulas and H. Bush, “Design, Construction, and Utilization of a Space Station Assembled from 5-Meter Erectable Struts,” NASA Struct. Interact. Technol., 1987]. The general approach is to use a multi-DOF industrial robotic arm mounted to a carriage which can traverse along an X and Y direction gantry system which encompasses the build area of the structure. This is what was used for a main example of a lattice building robot, the Automated Structures Assembly Laboratory developed at NASA Langley Research Center, which successfully demonstrated the viability of using robotic manipulators to automatically assemble and disassemble large truss structures [W. R. Doggett, “Robotic Assembly of Truss Structures for Space Systems and Future Research Plans,” in IEEE Aerospace Conference Proceedings, 2002]. This system successfully demonstrated the viability of using robotic manipulators to automatically assemble and disassemble large truss structures.
The use of robots to assist in the exploration and manipulation of structures has been an active topic of research for decades. Truss climbing robots are a form of climbing robot devoted to the traversal of three-dimensional truss structures [B. Chu, K. Jung, C. S. Han, and D. Hong, “A survey of climbing robots: Locomotion and adhesion,” Int. J. Precis. Eng. Manuf., vol. 11, no. 4, pp. 633-647, 2010]. Combined with a node design that can be robotically manipulated, such robots promise to provide an autonomous assembly, inspection, and reconfiguration platform for the creation of complex structures [P. J. Staritz, S. Skaff, C. Urmson, and W. Whittaker, “Skyworker: A robot for assembly, inspection and maintenance of large scale orbital facilities,” in Proceedings—IEEE International Conference on Robotics and Automation, 2001, vol. 4, pp. 4180-4185]. Locomotion strategies for previous robots have focused on treating the truss as a collection of struts and nodes [F. Nigl, S. Li, J. E. Blum, and H. Lipson, “Structure-reconfiguring robots: Autonomous truss reconfiguration and manipulation,” IEEE Robot. Autom. Mag., vol. 20, no. 3, pp. 60-71, 2013] [Y. Yoon and D. Rus, “Shady3D: A Robot that Climbs 3D Trusses,” in IEEE International Conference on Robotics and Automation, 2007]. The resulting robots combine 1-D translation along the length of strut with a method for transferring from one strut to another. This strategy is compatible with trusses that have an irregular geometry, at the cost of robotic complexity; in addition to doubling the translational degrees of freedom, performing a strut transfer also requires additional degrees of freedom, which move the relative position of the two translation mechanisms.
An alternative to the strut and node strategy is an approach called the “Relative Robot”. Relative robots, or robots which locomote and operate within a structured environment, are a new topic for research. Instead of strut-node networks, Relative Robots traverse a periodic structure, which allows translation with fewer degrees of freedom and enables increased reliability through fault-tolerant connection mechanisms. Examples include platforms such as the Automatic Modular Assembly System (AMAS) [Y. Terada and S. Murata, “Automatic assembly system for a large-scale modular structure—hardware design of module and assembler robot,” 2004 IEEE/RSJ Int. Conf. Intell. Robot. Syst. (IEEE Cat. No. 04CH37566), vol. 3, pp. 2349-2355, 2004], and usually the robot and structure are designed simultaneously as a whole system. Relative structure robots in general, and AMAS in particular, may not be suitable for space applications due to the density of the structure.
Recently, work has shown that modular structures built from lattice building blocks can result in structures with high stiffness to weight ratios [K. C. Cheung and N. Gershenfeld, “Reversibly assembled cellular composite materials.,” Science, vol. 341, no. 6151, pp. 1219-21, 2013], making them desirable for space applications [M. M. Mikulas, T. J. Collins, W. Doggett, J. Dorsey, and J. Watson, “Truss performance and packaging metrics,” in AIP Conference Proceedings, 2006, vol. 813, pp. 1000-1009]. There are numerous benefits afforded by this approach. One is that the building blocks can be reversibly assembled, disassembled, and reconfigured into other structural configurations [B. Jenett, D. Cellucci, C. Gregg, and K. C. Cheung, “Meso-scale digital materials: modular, reconfigurable, lattice-based structures,” in Proceedings of the 2016 Manufacturing Science and Engineering Conference, 2016]. The other is that the periodic lattice provides a structured environment in which a robotic platform can operate. This has potential advantages over traditional robotic construction systems which rely on a gantry-based build envelope [M. Carney and B. Jenett, “Relative Robots: Scaling AUtomated Assembly of Discrete Cellular Lattices,” in Proceedings of the 2016 Manufacturing Science and Engineering Conference, 2016]. In addition to being able to build arbitrarily large structures, a relative robot achieves metrology based on discrete lattice locations, rather than relying on global positioning systems or complex vision based systems [W. R. Doggett, “A Guidance Scheme for Automated Tetrahedral Truss Structure Assembly Based on Machine Vision,” 1996].
This invention describes a relative robotic platform for this modular lattice system, the Bipedal Isotropic Lattice Locomoting Explorer (BILL-E). Its design is specific to its tasks within the structured environment. This invention describes the lattice structure in which it operates, the functional requirements of its tasks, and how these inform the design of the robot. Further, this invention describes the prototype and investigates its performance analytically and with numerous experiments.
U.S. Pat. No. 7,848,838 to Gershenfeld et al. (U.S. application Ser. No. 11/768,176) describes a digital assembler for creating three-dimensional objects from digital materials made out of discrete components comprises an assembly head, error correction mechanism, parts feeder, and a controller ['838 Abstract]. U.S. Publication No. 20120094060 to Gershenfeld et al. (U.S. application Ser. No. 13/277,103) describes a digital material comprising many discrete units used to fabricate a sparse structure ['060 Abstract]. Neither the '838 patent nor the '060 publication disclose a bipedal isotropic locomoting explorer relative robot as described by this invention.